This invention relates to vacuum coating apparatus for coating substrates on all sides by rotation of the substrates in a material stream including a vacuum chamber having an elongated material source with a longitudinal axis and a transverse axis, a substrate rack provided with a plurality of fastening points for the planar disposition of a plurality of substrates above the material source in a substantially uniform distribution over the surface thereof, and a drive associated with the substrate rack for the production of a rotatory movement of the substrates.
The coating methods involved are the vacuum depositing method, the cathode spray method, the ion plating method, the chemical vapor deposition (CVD) method, and related methods.
It is known to provide substrates with a thin surface coating on all sides by subjecting them to a rotatory movement within a directed vapor stream and/or by passing them through the vapor stream while subjecting them to a rotatory movement. For this purpose the substrates can be mounted individually on shafts and brought into the vapor stream while rotating about the shaft axis. For the purpose of driving the shafts, gears or rollers are provided on the shaft ends and roll upon a stationary rack or rail. In the manner thus described, resistance coatings have been applied to tubular insulators; the known apparatus and methods of this kind, however, are limited to small substrates or to a small number of substrates.
It is also known to fasten geometrically simple substrates, such as optical lenses and filters, for example, on substrate racks or holders and to pass them periodically through the vapor stream while performing complex, composite movements. Such apparatus or methods are again suitable only for relatively small substrates whose shape presents no problems as far as a uniform distribution of the coating thickness is concerned.
The purpose of vapor depositing on large numbers of relatively complex parts, such as reflectors for motor vehicle headlights, for example, it is known to dispose the substrates on substrate holders or racks which are disposed for rotation within a substantially cylindrical cage. The vapor source is inside of the cage, so that, when the cage is rotated, the substrates are moved through the upwardly directed vapor stream. In this case, the substrate holders perform an additional rotatory movement within the cage based on a superimposed drive; this additional movement can be described as an involute movement. In the manner thus described, a very good distribution of the coating thickness is achieved on the basis of the law of probability. Such an apparatus, however, is not suitable for extremely irregularly shaped substrates of large dimensions, which are to be vapor coated in batches with high-melting metals or metal alloys, when the substrate temperatures are to be above, for example, 500.degree. C.
Examples of substrates of especially complex geometrical shape, in which great value is placed on a uniform coating thickness distribution, on the distribution of the alloy elements through the coating, and great strength of adhesion by intermetallic diffusion, are turbine blades for gas turbine engines, such as those used in aviation. The problems involved in the surface coating of such turbine blades are described in a publication entitled, "High Temperature Resistant Coatings for Super-Alloy" by Seelig et al of Chromalloy American Corporation, New York. It has hitherto been extremely difficult to produce such coatings with the required properties on a large industrial scale at economically acceptable prices. One special problem is the transmission of a defined rotatory movement from a drive motor to a plurality of substrates, and the relatively high losses of expensive vapor material which condenses on the internal surfaces of the vapor depositing apparatus rather than on the substrates, producing undesirable incrustation. This problem can be counteracted to a certain extent by a compact arrangement of the substrates in the vapor stream or above the evaporating crucible, as the case may be; the individual substrates, however, must not interfere with one another in performing their rotary movement.